Fix XMLHTTPRequest JS type in _loadHunk

sdk/lib/_internal/compiler/js_lib/js_helper.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library _js_helper;
 
 import 'dart:_async_await_error_codes' as async_error_codes;
 
 import 'dart:_js_embedded_names' show
     DEFERRED_LIBRARY_URIS,
@@ skipping 3528 matching lines @@
     }
   } else if (isWorker()) {
     // We are in a web worker. Load the code with an XMLHttpRequest.
     enterJsAsync();
     Future<Null> leavingFuture = completer.future.whenComplete(() {
       leaveJsAsync();
     });
 
     int index = uri.lastIndexOf('/');
     uri = '${uri.substring(0, index + 1)}$hunkName';
-    var xhr = JS('dynamic', 'new XMLHttpRequest()');
+    var xhr = JS('var', 'new XMLHttpRequest()');
     JS('void', '#.open("GET", #)', xhr, uri);
     JS('void', '#.addEventListener("load", #, false)',
        xhr, convertDartClosureToJS((event) {
       if (JS('int', '#.status', xhr) != 200) {
         failure("");
       }
       String code = JS('String', '#.responseText', xhr);
       try {
         // Create a new function to avoid getting access to current function
         // context.
@@ skipping 416 matching lines @@
   // This is a function that will return a helper function that does the
   // iteration of the sync*.
   //
   // Each invocation should give a body with fresh state.
   final dynamic /* js function */ _outerHelper;
 
   SyncStarIterable(this._outerHelper);
 
   Iterator get iterator => new SyncStarIterator(JS('', '#()', _outerHelper));
 }